Interaction between aquaculture and water quality in on-farm irrigation dams

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Irrigation dams in the Western Cape Province (WCP) have a history of enrichment through external factors such as agriculture (fertilizers and pesticides), runoff and storm water from the surrounding areas and effluent from infrastructure extension (housing and informal settlements). The incorporation of aquaculture into such dams adds additional nutrients to the water column and sediment although the nutrients are not very concentrated. Irrigation dams can play a role in providing water bodies for floating net cage farming systems. However, the research found that water quality analyses over the research period indicated that farm dams in the WCP overall had good water quality, indicating that commercial crop farmers are exercising better management practices. The water quality was generally within the South African Water Quality Guidelines for agriculture, aquaculture and recreational use. The introduction of aquaculture under the prevailing farm dam water quality guidelines generally did not pollute the water to such an extent that crop farming was compromised. Thus, there is a case to be made for promoting integrated aquaculture-agriculture farming. Sustainability for both uses can be maintained through robust site selection and diligent hands-on management of both fish and crop farming operations. This approach will ensure that commercial crop farmers’ irrigation regime and yield quality is not negatively affected. Recommendations include prevention or minimisation of pollution through aquaculture in irrigation farm dams by means of effective technology transfer and knowledge dissemination.